Fiber Bragg Gratings (FBG) sensors embedded in composite insulators used for electrical high voltage applications have been studied. The study included the design of a new method for the manufacturing of composite insulators with optical fibers. The instrumented prototype insulators are intended to keep track of the mechanical and thermal stresses endured by the insulators in actual operating conditions. Optical characterization of the FBG sensors have been made using an erbium laser source and a spectrum analyzer. A 5kN strain resolution in a temperature range between -40°C and +60°C has been achieved using standard SMF-28 optical fibers.